What is Single Sign-On (SSO) and Social Login: a complete guide

Single sign-on, better known as SSO, has become an essential part of the modern digital experience. It allows a person to identify themselves only once and, from then on, access multiple applications without repeating credentials. The convenience is enormous and, when implemented well, it also raises the bar for safety..

However, it's not all smooth sailing: if an SSO account falls into the wrong hands, the intruder could gain access to a large number of services. Therefore, SSO requires strong passwords, good security practices, and above all, multi-factor authentication to close additional doors for attackers..

What is SSO and why does it matter?

SSO is an authentication method whereby a user logs in once and gains access to multiple related but independent systems. The idea is simple: fewer passwords to remember, less friction, and a smoother experience across apps and websites.A typical example is the ecosystem of Googlewhere a login can open access to services like Gmail or YouTube without repeating credentials.

This approach fits within identity and access management frameworks, and is very often integrated with federated identity models. The result is a unified experience that, if designed intelligently, improves productivity without compromising security..

How it works: SP, IdP and the basic flow

SSO involves two main actors: the service provider, which is the application or site we want to enter, and the identity provider, which authenticates the user. Trust between both parties, orchestrated through standards and tokens, is at the core of the model.

1. The person accesses an application or site that acts as a service provider.
2. That provider sends an authentication request or token to the identity provider.
3. The identity system responds with the information needed to confirm SSO authentication.
4. When applicable, the user is asked to identify themselves and complete the required factors.
5. Once the credentials are validated, access is granted and that session is extended to other connected applications without restarting.

It is worth noting that SSO services do not usually store the full identity themselves; In general, they compare credentials with an underlying identity management service and issue or verify tokens..

OSH risks and how to mitigate them

The main risk is the domino effect: with compromised credentials, an attacker could access multiple applications at once. The first line of defense is long, complex passwords, well protected wherever they are stored..

Added to this is the almost unanimous recommendation from the industry: 2FA or MFA. Add an additional factor, such as a code on your mobile phone, a USB fingerprint reader or an identity document, drastically reduces exposure to stolen credentials.

SSO and multi-factor authentication: natural allies

SSO simplifies access, and multi-factor authentication adds layers of verification that block unauthorized access. Combining them offers a much stronger security posture with minimal impact on user experience.

Federated identity, SSO and same sign on

Federated identity management

Identity federation allows applications from different providers to share and validate identities through a common framework. This makes it possible for someone to log into one application and then access others without re-logging in when there is trust between domains..

SSO versus federation of identities

The federation is a broader umbrella for managing and authenticating identities across domains and providers. SSO is a specific functionality within that framework, which can be limited to services from a single provider or leveraged across multiple providers..

Same sign-on or same credentials

The concept of "same sign-on" refers to using the same synchronized credentials on different devices, as if it were a password manager that fills access points. It's not the same as SSO because it requires logging into each application, albeit with identical credentials..

SSO versus same sign on

In SSO, an initial authentication is sufficient to jump between related services; in same sign on, the user repeats the login each time, using the same keys. In practice, SSO reduces prompts and centralizes verification; same sign-on standardizes credentials but does not eliminate relogins.

Key protocols and technologies

SAML

This XML-based language describes how to package and transport authentication and authorization assertions between an identity provider and a service provider. SAML is popular in corporate environments and is very useful for Internet applications that speak the same standard..

SAML alone does not guarantee message integrity; it relies on complementary mechanisms such as digital signatures to ensure that the content has not been modified. Hence the importance of implementing signatures and rigorous validation of assertions.

Kerberos

Born at MIT within Project Athena, Kerberos defines a complete authentication and authorization architecture based on symmetric cryptography. It started with DES encryption and today adopts AES, offering longer keys and rounds that reinforce security.

Its symmetric key nature requires a trusted third party to manage keys and tickets, making it a perfect fit for corporate networks, LANs, and VPN. It is used less on the open internet, and in Microsoft environments it is the default option over NTLM..

OAuth 2.0

It is an authorization framework, not an authentication framework, designed to allow a client application to access protected resources on behalf of the user. The process involves the client, an authorization server that issues tokens, and the resource server that validates those tokens..

Permissions can be adjusted according to context or device type, varying scope and privileges. For example, a smart TV doesn't usually need the same level of access as a laptop..

Open ID Connect

OIDC adds identity management over OAuth, using JSON and REST services to be native to the Internet. It uses public-key cryptography and JSON web tokens, making large-scale integration and verification easier..

JWT

JSON web tokens are compact, signed, and suitable for sending in headers and URLs. They provide an ID token after authentication and access tokens for resources, with validation based on X.509 certificates..

JWTs are not encrypted by default, so they must travel over secure connections and must not include sensitive data. This pattern fits with REST architectures where state travels with each request.

LDAP

The lightweight directory access protocol was created to locate resources on a local network and store attributes of users and groups. It is not suitable for general internet use and its default authentication is weak without TLS protection..

It allows you to expand employee and belongings data, but it doesn't handle very detailed authorizations smoothly. Today it is combined with other layers to cover finer access control needs.

Authentication with smart card and passkeys

Smart card systems and passkeys rely on public-key cryptography, where a secure private key on the device signs transactions and a public key is shared for validation. Modern devices integrate TPMSecure Enclave or equivalents such as Android Knox for safeguarding keys.

If a device is lost and an attacker knows the owner's password, cryptography alone will not prevent the device from being used. Smart cards allow a reusable key pair to be transferred between devices using a reader or NFC. In the world of passkeys, there are already platforms that offer SDKs and components to integrate them with SSO in a very short time..

Cloud and on-premises SSO with Microsoft Sign In ID

In Microsoft Entra ID, the SSO option varies depending on how the application authenticates. Ideally, you should plan your strategy before creating or incorporating applications and use the application portal for easier management..

Federated

When SSO is configured between different identity providers, we call it federation. It is the most complete option, based on protocols such as SAML 2.0, WS Federation or OpenID ConnectIn this scheme, Microsoft Entra authenticates the user with their own account and the application trusts that result.

There are situations where the SSO option does not appear in an enterprise application: if the app has been registered through the application registrations section, authentication is configured with OpenID Connect and the option may not be displayed in the enterprise application navigation. In that case, OIDC relies on OAuth 2.0 to authorize without exposing credentialsAdditionally, it will not be available when the app resides with another tenant or when the account does not have sufficient permissions as a cloud application administrator, application administrator, or service entity owner.

Password-based

Local applications can opt for password-based SSO, especially when using Application Proxy. After the first login with username and password, the system securely reproduces the credentials via a browser extension or mobile appThis is useful when you want to take advantage of the existing login in the application and allow an administrator to manage passwords without the user knowing them.

Linked

Linked login helps provide a consistent experience during a migration. It allows you to publish links to different applications on the portal, although it doesn't offer true SSO through Microsoft LoginIn this case, MFA and conditional access cannot be applied to the linked app, and an account must exist in the target application, provisioned automatically or manually.

Disabled

When SSO is disabled, users may have to authenticate twice, first on Microsoft Sign In and then on the application. This is a valid option if the app is not yet going to be integrated, is being tested, or you want to force authentication on a local application that did not require it.Note: If the app uses provider-initiated SAML and SSO is disabled, users may still be able to log in outside the application portal; to prevent this, the user's login capability must be disabled.

To apps In the cloud, federation protocols are recommended. In local environments, Application Proxy facilitates remote access and secure publishing. The choice of method will depend on where the app is hosted, how it routes traffic, and what protocols it supports..

User experience and application portal

Most users want to log in and start working without thinking about protocols. The application portal, known as My Applications, centralizes access and reduces the need to continually enter passwords..

IdP initiated vs. SP initiated

In an identity provider-initiated flow, the session starts from the IdP issuing an assertion to the service provider. If initiated by the SP, the user first accesses the app, which redirects them to the IdP to authenticate and return securely..

Social Security: advantages and precautions

Platforms like Google, Facebook LinkedIn allows you to use your credentials to access third-party services. The convenience is undeniable, but a vulnerability in the social media platform could have a domino effect on other linked accounts; for example, see how Report your Gmail login.

Company SSO and web SSO

In large organizations, enterprise SSO or eSSO operates within the boundaries of the corporate network. You can rely on symmetric encryption, prefer SAML, and combine multiple authentication factors for more secure devices and access.With the rise of SaaS applications, companies are deciding between adopting more internet-oriented frameworks like OAuth or requiring these apps to be integrated into their corporate structure; many accept both approaches.

For public web applications, the OAuth plus OpenID Connect combination is usually the natural choice. They are widely accepted standards, designed to scale across multiple domains and aligned with modern development expectations..

Zero Trust, adaptive policies and best practices

Robust SSO systems incorporate contextual checks and risk-based policies: location, device, network security posture, or usage habits. Applying risk-based MFA and making adaptive decisions helps align SSO with the Zero Trust approach.

Regarding data protection, communications must be encrypted with strong algorithms such as AES 256 or RSA 2048, in addition to signing tokens and assertions. User training, the definition of clear policies, and periodic audits complete the operational security triangle..

SSO and Active Directory: Key Differences

SSO is an access control property that allows a user to authenticate once and access multiple related systems without re-entering credentials. Active Directory, for its part, is a directory service that centralizes information, policies, and security in an infrastructure Windows.

AD is queried and managed through LDAP and is used to organize users, computers, groups, and permissions on a large scale, from small networks to large deployments with multiple domains. While AD stores and governs identity, SSO orchestrates seamless access between applications by leveraging that identity..

SSO offers convenience and cleaner access management, but requires protecting the master key with MFA and risk-based controls. Protocols such as SAML, OAuth, and OpenID Connect, along with technologies like Kerberos, JWT, LDAP, and smart cards, allow for the construction of solutions that work locally, in the cloud, and at large scale without compromising security..